"While at this time we are confident that the information extracted does not enable a successful direct attack on any of our RSA SecurID customers, this information could potentially be used to reduce the effectiveness of a current two-factor authentication implementation as part of a broader attack," Coviello said.

The cyber-attack was "recent" and was a so-called Advanced Persistent Threat incident, Coviello said. This is the type of attack that compromised systems at Google and as many as 100 other companies in late 2009. Hackers use e-mail-based or Web-based attacks to get a foothold in the company and then move about the company's internal networks looking for sensitive data to sneak out.

In this case, the hackers found information on RSA's SecurID products -- which are used on PCs, USB devices, phones and key fobs in about 25,000 corporations to provide an extra layer of security beyond a username and password for people logging into programs or networks.

Having access to RSA's internal networks and the SecurID source code might give criminals some subtle way of attacking SecurID users, but it shouldn't give them a way of completely breaking RSA's encryption, said Thorsten Holz, an assistant professor at Ruhr-University Bochum who studies computer security. "If RSA implemented everything correctly, nobody should be worried too much," he said.

If RSA's hackers were somehow able to obtain the cryptographic keys known as seed records, which are installed on SecureID tokens, then things could be much worse, according to Thierry Zoller, a security practice lead with a European consulting company. That's because these seed records are used to generate the unique, one-time passwords that SecureID generates every 30 seconds or so in order to authenticate the user. "If the attacker has access to the seed, he potentially can calculate the number that is shown on the token during authentication," Zoller said.

With SecureID passwords in hand, the bad guys would still need regular user name and passwords to log into to the network or program they were trying to compromise, but the cracking job would now be much easier.

However, from RSA's statement, it's not clear exactly what the hackers were able to learn off the company network.

According to Nate Lawson, a cryptographer and the founder of Root Labs, there's simply not enough information available to tell how bad the problem really is. "If I was a customer of theirs it makes it really hard to know what I need to do. They recommend a lot of things that people are already doing," he said.

No EMC products were affected by the attack and RSA doesn't think other RSA products are affected. Also, there's no evidence that customer or employee information was compromised, Coviello said.

EMC's stock [EMC] was down 1.25 percent in after-hours trading following the news. In a regulatory filing, EMC said it "does not believe that the matter described in the letter and note will have a material impact on its financial results."